USDA Plant Hardiness Zones & Average Annual Extreme Minimum Temperature (1977-2005)

Table and information from http://planthardiness.ars.usda.gov/PHZMWeb/

Zone Fahrenheit Example Cities
1a −60 to -55 °F
1b -55 to -50 °F Fairbanks, Alaska;   Resolute, Northwest Territories (Canada)
2a -50 to -45 °F Prudhoe Bay, Alaska;   Flin Flon, Manitoba (Canada)
2b -45 to -40 °F Unalakleet, Alaska;   Pinecreek, Minnesota
3a -40 to -35 °F International Falls, Minnesota;   St. Michael, Alaska
3b -35 to -30 °F Tomahawk, Wisconsin;   Sidney, Montana
4a -30 to -25 °F Minneapolis/St.Paul, Minnesota;   Lewistown, Montana
4b -25 to -20 °F Northwood, Iowa; Nebraska
5a -20 to -15 °F Des Moines, Iowa;   Illinois
5b -15 to -10 °F Columbia, Missouri;   Mansfield, Pennsylvania
6a -10 to -5 °F St. Louis, Missouri; Lebanon, Pennsylvania
6b -5 to 0 °F McMinnville, Tennessee;   Branson, Missouri
7a 0 to 5 °F Oklahoma City, Oklahoma;   South Boston, Virginia
7b 5 to 10 °F Little Rock, Arkansas;   Griffin, Georgia
8a  10 to 15 °F Tifton, Georgia;   Dallas, Texas
8b 15 to 20 °F Austin, Texas;   Gainesville, Florida
9a 20 to 25 °F Houston, Texas;   St. Augustine, Florida
9b 25 to 30 °F Brownsville, Texas;   Fort Pierce, Florida
10a 30 to 35 °F Naples, Florida;   Victorville, California
10b 35 to 40 °F Miami, Florida;   Coral Gables, Florida
11a 40 to 45 °F Honolulu, Hawaii;   Mazatlan, Mexico
11b 45 to 50 °F
12a 50 to 55 °F
12b 55 to 60 °F
13 60 to 65 °F
13b 65 to 70°F

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